Aircraft and other machinery employ seals to control air flow between static and moving parts within the machinery. In particular, in gas turbine engines seals are located in numerous locations such as on rotors, turbines, etc., so as to provide cavities for transitioning fluids to pass therethrough. The transient response of the seal performance can result in fluctuations in pressure within the cavities and in the flows into and out of the cavities. This arrangement can result in additional cooling flow entering the gas path hence reducing engine efficiency and increasing gas path temperatures. This combined with fluctuations in the feed pressure and temperature to cooled turbine blades may result in reduced lives for turbine components. The fluctuations in pressure may also result in a transient increase in the axial load on the thrust bearing locating the engine shaft. Such concern may cause the bearing to have a reduced life or increase its risk of failing.
To prevent undesired radial leakage between concentric streams of fluid, labyrinth seals are used for air-air and air-oil axis-symmetric seals. Labyrinth seals may use a stair-step configuration to discretize partially radial cavities into quasi axial cavities. These seals require close-operating radial clearances in order to accomplish satisfactory sealing. As a result, it is necessary to use extremely accurate manufacturing and assembly techniques which are expensive and time consuming in order to provide acceptably small radial seal clearances at the time of assembly.
Gas turbine engines may also employ seals such as carbon seals which are used almost exclusively for low radius shaft or sump air-oil seal applications, due to the need for cooling of carbon seals in general and the difficulty in manufacturing high radius carbon seals. Carbon seals can also seal in the radial orientation; however, carbon seals must be cooled, usually with oil, on at least one side and become less effective at higher radii and/or lower cooling levels. Such systems require many components and are costly to design and manufacture.
In labyrinth seal embodiments having fins at multiple radii, a load is applied to both rotating members of the seal due to the pressure in the cavity between the fins. The load on the rotor will ultimately be carried by a bearing. It would be helpful to minimize the total load carried by the bearing at all conditions to increase bearing life, enable the use of a smaller bearing, and reduce the heat generated by the bearing. Controlling the load generated in embodiments with fins at multiple radii is one way to accomplish this task, which is one subject of this disclosure.
During operation, mechanical and thermal movements of the gas turbine engine cause relative movement of the sealed components. Thus, the distance between the abutting surfaces of the labyrinth seal changes throughout operation. This can result in periods during operation where the lining and fins are sufficiently close that the air flow through the seal is restricted to an unacceptable level. In the case where the seal has to allow a certain level of purging air flow through the seal, restriction of the low pressure through the seal can lead to hot gas integration causing damage or failure of engine parts.
It would be helpful to solve the problems of radial cavities with labyrinth seals, air-air seals with carbon seals, and high radius seals with carbon seals. It would also be helpful to provide a sealing system and construct that increases performance over standard labyrinth seals, especially at high radii, while utilizing less axial space.
It would further be helpful to provide an enhanced sealing construct that decreases specific fuel consumption and overcomes the poor performance of current high radius seals.